Page | 002 There are four basic cell designs; button/coin cells, polymer/pouch cells, cylindrical cells, and prismatic cells. (see Figure 1).
Figure 1. Typical Cell Designs
The most common designs prevalent in academic and research use include polymer/pouch cells typically used in iPods, tablets and cell phones. Cylindrical cells incorporate the similar design parameters that have been the standard for alkaline cells for years (A, AA, AAA, C, and D cells). Prismatic cells are thin, square cells with hard steel cases. Prismatic cells are typically used in cell phones and thin, laptop computers.
Other than cell phones and tablets, most portable electronic/electrical devices operate above the normal operating voltage of single lithium-ion batteries (3.6–4.2V). For such devices, numerous cells connected in packs provide the desired voltage and capacity. Connecting cells in parallel increases pack amperage and discharge capacity while connecting cells in series increases pack voltage. As an example, a 24V lithium-ion battery pack typically has six cells connected in series.
Many battery packs have built-in circuitry used to monitor and control the charging and discharging characteristics of the pack. As an example, circuitry will automatically manage the charging when the pack cells reach 4.2V and/or if the temperature exceeds a preset value. The circuits will shut down the pack if the cells discharge below a preset value (e.g., 3.3V per cell).
The cylindrical cell (identified by “18650”) is similar in size and shape to an AA battery. It is the “workhorse” of the lithium-ion battery industry and is used in a majority of commercially available battery packs. Examples are shown in Figure 2.
Figure 2. Battery/Battery Pack Examples
LITHIUM-ION BATTERY HAZARDS
Lithium-ion battery fire hazards are associated with the high energy densities coupled with the flammable organic electrolyte. This creates new challenges for use, storage, and handling. Studies have shown that physical damage, electrical abuse such as short circuits and overcharging, and exposures to elevated temperature can cause a thermal runaway. This refers to rapid self-heating
Page 2 of 6 | November 2021 | www.ehs.washington.edu | Lithium-Ion Battery Safety
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